The present invention relates to a high frequency signal receiving device. Particularly, the present invention can miniaturize a high frequency signal receiving device that can receive the broadcast waves of terrestrial digital television broadcast and terrestrial analog television broadcast by including: reference frequency signal generating means for generating a reference frequency signal; high frequency signal processing means for obtaining a signal of a desired channel from a high frequency signal obtained by receiving a broadcast wave, using the reference frequency signal; analog demodulating means for subjecting the signal obtained by the high frequency signal processing means to an analog demodulation process; and digital demodulating means for subjecting the signal obtained by the high frequency signal processing means to a digital demodulation process using the reference frequency signal.
With recent enhancement of functionality of portable devices, the portable devices can receive the broadcast waves of terrestrial analog television broadcast. FIG. 4 is a diagram showing a configuration of a high frequency signal receiving device used to receive the broadcast waves of terrestrial analog television broadcast.
A high frequency signal obtained by receiving a broadcast wave by a broadcast receiving antenna 51 is amplified to a predetermined signal level by a high frequency amplifier 52-1 in a high frequency signal processing unit 52, and then supplied to a first mixer 52-2. The first mixer 52-2 generates a first intermediate frequency signal of a few GHz by multiplying the signal supplied from the high frequency amplifier 52-1 by an oscillating signal having a frequency corresponding to a selected channel from a first local oscillator circuit 52-3. This first intermediate frequency signal is band-limited by a SAW filter (surface acoustic wave filter) 53, and thereafter supplied to a second mixer 52-4. The second mixer 52-4 generates a second intermediate frequency signal by multiplying the signal supplied from the SAW filter 53 by an oscillating signal supplied from a second local oscillator circuit 52-5. An amplifier 52-8 amplifies the second intermediate frequency signal to a predetermined signal level. The amplifier 52-8 supplies the second intermediate frequency signal to an analog demodulating unit 55 via a SAW filter 54. An intermediate frequency amplifier 55-1 in the analog demodulating unit 55 amplifies the second intermediate frequency signal. The intermediate frequency amplifier 55-1 supplies the amplified second intermediate frequency signal to a video detector 55-2. The video detector 55-2 generates a detection output signal by multiplying the second intermediate frequency signal by an oscillating signal that is supplied from an oscillator circuit 55-3 and has a frequency equal to that of a video carrier. The video detector 55-2 supplies the detection output signal to a low-pass filter 55-4 and a band-pass filter 55-6. The low-pass filter 55-4 obtains an analog video signal by extracting only a low frequency component from the detection output signal. The low-pass filter 55-4 outputs the analog video signal via a video output amplifier 55-5. The band-pass filter 55-6 extracts only a signal component in a predetermined band from the detection output signal. The band-pass filter 55-6 supplies the signal component to an FM detector circuit 55-7. The FM detector circuit 55-7 outputs a baseband analog audio signal obtained by subjecting the signal supplied to the FM detector circuit 55-7 to a detection process. The first local oscillator circuit 52-3 is connected with a PLL circuit 52-6, and the second local oscillator circuit 52-5 is connected with a PLL circuit 52-7. The PLL circuits 52-6 and 52-7 control the oscillating signals generated by the first local oscillator circuit 52-3 and the second local oscillator circuit 52-5 to a desired frequency, using a reference frequency signal generated by a reference frequency signal generating unit 56.
The thus formed high frequency signal receiving device is included in a card-shaped case, as shown in Japanese Patent Laid-Open No. Hei 5-14133, for example. Thus, by only inserting the card-shaped high frequency signal receiving device into the card slot of a portable device, a television broadcast receiving function can be easily added to the portable device.
In broadcast using ground waves, in addition to terrestrial analog television broadcasting, terrestrial digital television broadcasting using an ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) has started. This terrestrial digital television broadcasting uses an OFDM (Orthogonal Frequency Division Multiplexing) system to reduce effects of disturbances caused by multipath (delayed wave) interference, interference from an adjacent channel, and the like. A transmission band of one channel (a frequency bandwidth of 6 MHz) is divided into 13 segments (the bandwidth of one segment is 6/14 MHz). Transmission parameters and information to be transmitted are set in each segment so as to enable high-definition broadcasting, a plurality of standard-definition broadcasts, and terrestrial digital television broadcasting suitable for reception by cars and reception by portable terminals. A central segment of the 13 segments is provided for portable and mobile reception. By performing narrow-band reception in which only the central segment is received, a terrestrial digital television broadcast can be viewed easily on a portable device and the like.
FIG. 5 shows a configuration of a television receiving device used to receive a terrestrial digital television broadcast. A high frequency signal obtained by receiving a broadcast wave by a broadcast receiving antenna 51 is amplified to a predetermined signal level by a high frequency amplifier 57-1 in a high frequency signal processing unit 57, and then supplied to a mixer 57-2. The mixer 57-2 generates an intermediate frequency signal by multiplying the signal supplied from the high frequency amplifier 57-1 by an oscillating signal having a frequency corresponding to a selected channel from a local oscillator circuit 57-3. The mixer 57-2 supplies the intermediate frequency signal to a digital demodulating unit 58 via an amplifier 57-4. An A/D converter circuit 58-1 in the digital demodulating unit 58 converts the intermediate frequency signal into a digital signal. The A/D converter circuit 58-1 supplies the obtained digital signal to an OFDM demodulator circuit 58-2. The OFDM demodulator circuit 58-2 supplies a demodulated signal obtained by performing OFDM demodulation to a demodulated signal processing circuit 58-3. The demodulated signal processing circuit 58-3 subjects the demodulated signal to an error correction process or the like. The demodulated signal processing circuit 58-3 then outputs the signal as a transport stream. Thus, the high frequency signal processing unit 57 uses a single conversion system, and therefore saves more power than a terrestrial analog television broadcast receiving device using a double conversion system. The local oscillator circuit 57-3 is connected with a PLL circuit 57-5. The PLL circuit 57-5 controls the oscillating signal generated by the local oscillator circuit 57-3 to a desired frequency, using a reference frequency signal generated by a reference frequency signal generating unit 59. The digital demodulating unit 58 operates using a clock signal supplied from a clock signal generating unit 60.
Terrestrial analog television broadcasting has a problem in that a ghost or the like tends to be caused by a delayed wave and disturb a screen in urban districts of a metropolitan area. In addition, a screen tends to be disturbed when a receiving device receives the broadcast wave of a terrestrial analog television broadcast while moving.
On the other hand, terrestrial digital television broadcasting can reduce effects of a delayed wave by inserting guard intervals even when the delayed wave occurs. Terrestrial digital television broadcasting therefore provides images of good quality even when a receiving device receives the broadcast wave of a terrestrial digital television broadcast in an urban area or when a receiving device receives the broadcast wave of a terrestrial digital television broadcast while moving. However, terrestrial digital television broadcasting is performed only in certain areas for the time being. Therefore a mobile device supporting only terrestrial digital television broadcasting cannot receive a television broadcast wave when moving from an area.
Accordingly, it is desirable to provide a high frequency signal receiving device that has a function of receiving terrestrial analog television broadcasts and terrestrial digital television broadcasts and can be miniaturized.